Replica plating of cellular colonies is a widely used technique in molecular biology and genetics. The process of replica plating involves a printing-like transfer of a set of colonies from one culturing surface (such as a gel medium in a Petri dish) to another culturing surface or surfaces. The transfer process is performed by contacting colonies with a sterile transfer pad to which some of the cells from each colony adhere, and then contact printing these cells onto one or more additional culturing surfaces to deposit some of the cells. This technique was originally described by Lederberg et al., J. Bacteriology 63:399 (1952) where 12 cm squares were cut from velveteen yardage and a square placed nap up on a cylindrical wood or cork support, and held firmly in place by a metal flange or hoop pushed over the fabric and around the rim of the support. An agar plate carrying the initial colonies was inverted onto the fabric with slight digital pressure to transfer the cells from the culturing surface. The imprinted fabric provided the pattern for transferring replica inoccula to subsequent plates impressed in the same way. This technique is still commonly used today with the fabric squares being washed, sterilized, and used repeatedly. When the fabric squares are first prepared from new fabric, they must be washed one or more times to remove chemicals within them that are inhibitory to colony growth.
Curtis et al., Biotechniques 152 (March/April 1985) describe a replica plating colony transfer pad. They state that velvet is of limited use for such a pad because its preparation is labor intensive, and the quality and quantity of replicates that can be obtained is restricted. They mention that a number of other materials, such as nitrocellulose and nylon membranes, are now commonly used, and that each have positive and negative attributes. Toothpicks and microloops also continue to be used for transfer of individual colonies. The authors state that a convenient, ready to use device is provided consisting of a laminated polyurethane foam pad coated with a water absorptive film.
Provonchee, U.S. Pat. No. 4,717,667, describes a replica plating device having a rigid layer, and a transfer surface formed from an open cell flexible foam, including a hydrophilic layer. Provonchee states that a resilient backing layer is one of the essential elements of the device. This backing layer is resilient to deform at least generally in response to the surface contour of the growth medium on which the cells to be transferred are supported. Provonchee states that the conventional velvet pad has certain limitations. The velvet pad is essentially a series of needle tips in a fixed array, with the spaces between the needle tips serving as a collector of moisture which the pad soaks up when contacted with a growth medium. It is necessary that such moisture be accommodated, lest lateral smearing of replicate colonies result. However, Provonchee states that the colony transfer surface of his device may be chosen from conventional cut pile velvet, which may be bonded to the resilient backing layer with a water-based latex binder.
Maniatis et al., Molecular Cloning and Laboratory Manual, Cold Spring Harbor, 1982, on pages 304-306 describe use of a conventional replica plating tool, having velvet at its transfer surface, for replica plating phase particles to nitrocellulose paper.
Sapatino, U.S. Pat. No. 4,634,676, describes a replica plating device having a hooked skirt extending over the rim of a culture container and downwardly over this rim to prevent excessive movement of the pressing surface within the container. This skirt does not appear to prevent contact between the side wall of the replica plating device and the inside wall of the culture dish container. The device includes a compressible material, for example, velvet, which serves to cushion the pressing effect of the replica plating device against the cells and culture medium during use. This compressible material may be adhesively attached to the exterior surface of the bottom wall of the replica plating device.